Systems are known for picking up and carrying material such as planks, sheet metal plates, or similar materials. Such systems comprise a structure mounted to move along a frame and including a pick-up head that operates by suction.
In known systems, the suction pick-up head comprises a box connected to a suction device, generally a turbine, carried by the frame of the system. The box of the pick-up head has a soleplate supporting rows of independent compartments each having a bottom orifice opening out in the bottom face of the soleplate and a top orifice fitted with a moving closure member mounted in the compartment to enable the top orifice to be closed when the bottom orifice is not obstructed by an article to be picked up and the suction is sufficient to suck up the valve member. When the bottom orifice of the compartment is obstructed by an object to be picked up, the valve member remains open and the suction inside the box then serves to press the object against the soleplate of the pick-up head. To provide better sealing of the contact between the soleplate and the article to be picked up, it is preferable to provide a sealing material on the underside of the soleplate, such as a foam, whose characteristics are adapted to the surface state of the articles to be picked up.
Such a structure enables objects to be handled that have a variety of dimensions even when said objects occupy only a portion of the surface of the soleplate of the pick-up head. When it is desired to be able to pick up a multiplicity of articles of small dimensions or articles of various outlines, it is necessary to subdivide the surface of the soleplate into a very large number of compartments that are likewise of small dimensions so as to ensure that each article can fully obstruct the bottom orifice of a number of compartments that is large enough to enable the article to be picked up.
Furthermore, in order to be able to maintain sufficient suction in the compartments in register with articles to be picked up, it is necessary for all of the moving closure members of the compartments which are not in register with an article to be picked up to close very quickly when picking up articles. Raising each closure member so as to press it against the top orifice of the corresponding compartment requires a certain flow rate to pass through the top orifice of the compartment. When the closure members of a large number of compartments need to be raised because of the small surface area of the articles to be picked up, it is therefore necessary to provide a large suction flow rate through the box. However, to provide sufficient lifting force for the articles to be handled, it is necessary to cause the suction turbines to operate in a mode that provides a large amount of suction but at a small flow rate that does not make it possible simultaneously to raise a large number of closure members.
To mitigate that drawback, pick-up heads are known that have a buffer volume connected to the box containing the pick-up compartments, with a shutter being located to separate the buffer volume from the box until a certain level of suction is obtained in the buffer volume. Opening the shutter then allows suction at a rate that is proportional to the size of the buffer volume. To provide a large flow rate, it is therefore necessary to provide buffer volumes of large dimensions. This implies not only that the pick-up head needs to be large in size, but also that it needs to be heavy, both of which needs constitute major drawbacks for a moving structure. In addition, such suction through all of those compartments which are not in register with articles to be picked up causes a large amount of dust to be sucked up, which dust is subsequently deposited inside the box, where it piles up and impedes proper operation of the pick-up head. In addition, sudden decompression of both the box and the buffer volume when the articles are put down gives rise to a loud noise which degrades working conditions for the operators of the pick-up system.